There is a reactor as one of parts of a circuit for performing operations of stepping-up and -down a voltage. In one form of a reactor employed, for example, in a converter that is loaded on a vehicle such as a hybrid car, a pair of coils, each formed by spirally winding a wire, are disposed side by side around respective portions of a magnetic core having a annular shape, e.g., an O-like shape (Patent Literature (PTL) 1).
A small reactor including only one coil is also known like a reactor disclosed in PTL 2. Such a reactor includes, as illustrated in FIG. 1 of PTL 2, the so-called pot type core, i.e., a magnetic core including a columnar inner core portion arranged inside a coil, a cylindrical core portion covering substantially an entire outer peripheral surface of the coil, and a pair of disk-shaped core portions arranged at respective end surfaces of the coil. In the pot type core, the concentrically-arranged inner core portion and cylindrical core portion are coupled to each other by the disk-shaped core portions, thereby forming a closed magnetic circuit.